Will everything get translated?
An international site should ensure that all alt text is translated along with the rest of the content. After all, the end user may well be using a screen reader or other assistive technology to access the site, in a different language to the default. I wonder how many multi-lingual sites actually manage to maintain this good practice. I am also wondering how I can convince my clients to be that thorough with their translations.
Just checked the BBC News site and as I expected, they are meticulous in their management of translations. Every picture has language specific alt text. Of course much of this depends on the level of sophistication of the content management system and the controls in place to ensure such a high level of accessibility.